Heat Exchanger and Applications Thereof

ABSTRACT

A heat exchanger for exchanging heat between a liquid-containing medium and a gas comprises a medium inlet and a medium outlet and a flat heat exchanger mat, wherein the mat comprises a number of parallel, equidistant capillaries of heat-conducting material and wires of heat-conducting material which are attached in heat-conducting contact to the capillaries, extend in transverse direction relative thereto and have a mutual distance in the order of magnitude of the diameter of the wires, wherein gas can flow along the wires for heat exchange between this gas and the medium flowing through the capillaries, and wherein the gas flows along the mat and at least a substantial part of the gas is prevented from flowing through the mat, and the gas flows in longitudinal direction of the wires.

The invention relates to a heat exchanger according to the heading ofclaim 1.

Such a heat exchanger is known for instance from JP-A-61-153388 (Kokai)and from EP-A-0 735 328.

In the heat exchangers known from these publications the gas flowsthrough the openings of the mat formed by the capillaries and the wires.As a result the gas flowing through the heat exchanger undergoes aconsiderable flow resistance. This flow resistance must be overcome byguiding the gas flow through the heat exchanger under the influence offan means. The electric power required for this purpose results in anundesirable effective reduction in the performance of the heatexchanger.

In the known heat exchangers it is in addition not possible to preventdust accumulating in the mats within a very short time. The heatexchanger hereby becomes blocked in a very short time. The designperformance can be temporarily restored again only by maintenance orblowback of gas, and thus cleaning of the mat.

It is an object of the invention to greatly improve the performance ofthe heat exchanger of the described type and to make the heat exchangersubstantially maintenance-free.

With a view hereto the invention provides a heat exchanger of thedescribed type which has the feature of claim 1.

A possible practical embodiment of the heat exchanger is specified inclaim 2.

Claim 3 relates to the possibility of connecting the wires to thecapillaries by means of a weaving process according to the teaching ofthe invention.

Claim 4 relates to an alternative wherein the wires are not connected tothe capillaries by means of a weaving process, but wherein the wires areattached to the capillaries in mutually parallel relation on either sideof these capillaries. Compared to the structure according to claim 3,the structure according to claim 4 has the great advantage that thecentre-to-centre distance between the capillaries can be considerablysmaller, which improves the performance of the heat exchanger stillfurther. In the case of claim 3 for instance the heat exchanger can meetthe specification as according to claim 13, and in the case of claim 4the heat exchanger can meet the specification of claim 14.

Claim 5 relates to the possibility of parallel connection of groups ofin each case a number, preferably an equal number, of capillaries andcollective connection thereof to respectively an inlet manifold and anoutlet manifold of the group. The inlet manifold can also form part ofthe outlet manifold of a preceding group of capillaries, while theoutlet manifold can form part of an inlet manifold of a following groupof capillaries. It will be apparent that the relevant aligned manifoldsmust be thermally separated from each other, because there is after alla temperature difference between the two during operation.

An important alternative is specified in claim 6. In this embodiment thecapillaries are connected in series to each other, no use is made of aninlet manifold and an outlet manifold and the medium in adjacentcapillaries flows in mutually opposite directions. This embodimentprovides a greater flow resistance to the through-flowing medium thanfor instance the embodiment of claim 5, but has the advantage of beingable to suffice with a very small volume of medium. Particularly in thecase where this medium has harmful or hazardous properties, such as CFCsfor air-conditioning systems, propane and the like, the quantity ofmedium in a heat exchanger, even if it comprises a plurality of mats,can be negligible and amount to for instance only a few tens ofmillilitres. In the embodiment where use is made of manifolds thequantity of medium present in the heat exchanger is substantiallygreater, for instance in the order of litres. It is conceivable thatsuch a heat exchanger does not even meet the requirements set down bylegal regulations, and it is therefore not suitable for the relevantapplication.

Claim 7 describes that the embodiment according to claim 6 requiresmechanical strengthening in some circumstances, since a zigzag-modelledcapillary tube does after all only have a very limited mechanicalstiffness.

The embodiment according to claim 8 relates to a practical aspect of theinvention. The perforations can be arranged in any suitable manner inthe relevant tube. Use can for instance be made of drilling, piercingwith a punch or the like, or flow drilling. Instead of a tube, the airduct wall can also be provided with slit-like holes not extendingthrough the wall, for instance by vacuum-forming or injection moulding,into which the U-bends fit so that the mats become stiff and havemutually equal interspacing.

An important further development of claim 6 or 8 is described in claim9. The hard-soldering can take place by local heating to a temperaturein the order of 500 to 800° C. A very strong connection is herebyobtained in very simple and per se known manner which can withstand thehigh pressures in the order of 15-20 bar which occur in compressorcoolers and air-conditioning systems. The same advantage is obtainedwith the embodiment of claim 6 which owing to its nature can veryreadily withstand said occurring high pressures.

Claim 10 relates to a pretreatment which is recommended. Said anodictreatment is an example. Other possible tin-stripping methods can alsobe considered. Said anodic treatments can however be performed verysimply, rapidly and reliably.

An embodiment which is very suitable in applications where only limitedrequirements are made of the pressure resistance and complete sealing isspecified in claim 11.

Claim 12 gives a possible and practical dimensioning of the capillaries.

Claim 15 gives the possible dimensioning of the wires. Tin-plated copperwires are particularly envisaged. Copper is a material with a highcoefficient of heat conduction. In this sense silver wires would be evenbetter, but silver has the drawback of being considerably moreexpensive. Aluminium could also be suitable for the heat-conductingwires. Aluminium has the drawback however of having a heat conductioncoefficient which, while being good, is still lower than that of copper.In addition, it is difficult to connect aluminium wires in reliablemanner and in metallic contact to the capillaries in heat conductivemanner. In the case of tin-plated copper this can be easily realizedwith a soldering process. During the production process a mat consistingof capillaries and wires of tin-plated copper can thus be heated toabove the melting point of the tin. The adhesion at the contact zones ishereby brought about by soldering.

Claim 16 relates to an important aspect which states in essence that theheat exchanger can be operated in counter-flow. As is known,counter-flow provides the greatest efficiency, greater than crossflowsuch as is known from, among others, the earlier publications referredto at the beginning of this specification. In respect of claim 16 itmust of course be appreciated that there is no counter-flow in thestrict sense of the word, but an “effective” counter-flow wherein thecapillaries do extend in transverse direction relative to the flowdirection of the gas but adjacent capillaries have a difference intemperature corresponding to counter-flow.

The heat exchanger according to claim 17 comprises a number of mutuallyparallel mats. It will be apparent that the inlet of each mat must beconnected to the inlets of the other mats, for instance by a shared maininlet manifold. The outlets of the mats must be connected to each otherby means of a main outlet manifold.

Claim 18 relates to the heat exchanger of claim 17. According to claim18, the spacers can be the manifolds. To the extent there are localtemperature differences between the manifolds, these must be thermallyinsulated from each other. The mats and the associated manifolds arehowever preferably identical and connected in parallel to each other inall respects. There need then be no fear of unintentional heat transferand thermal insulation between the manifolds is not therefore necessary.

In per se known manner the spacers according to claim 17 and themanifolds of claim 18 can be held against each other. The mats can forinstance be formed into a stack and the spacers are pressed against eachother by means of clamping means.

Claim 19 relates to the heat exchanger according to claim 7. This has nomanifolds but strengthening profiles on either side of the mat. Thesecan also serve as spacers. An air duct wall can also be dimensioned inwhich slits hold the U-bends of the capillaries in their position.

Claim 20 provides the option of a forced drive of the gas flow.

Claim 21 gives a variant operating wholly without external energy. TheCO₂-containing exhaust gases of a combined heat and power plant areoften admitted into a greenhouse in order to enhance plant growth. Theflow impulse of these gases can be used to support the natural draughtthrough the heat exchanger.

According to the prior art, commercial greenhouses are cooled duringsunshine hours by opening windows in the roof. This is effective notonly in replacing hot inside air with cooler outer air, but also inproviding the plant culture with the possibility of evaporating water byreplacing moist inside air by drier outside air. The opening ofgreenhouse windows does however involve the risk of infection with or byflying insects, and results in the loss of practically all irrigationwater that the plants need.

It is possible to keep the windows closed and to cool the greenhousewith water, for instance groundwater. This groundwater is heated in theglasshouse and must be cooled again, for instance at night or in thewinter, such that it is possible to store the heat absorbed from thegreenhouse when cooling is necessary. For this method of operation aheat pump is normally used, such as in air-conditioning systems, whichaccording to the prior art are equipped with standard heat exchangershaving pipe bundles with plate fins through which heat exchanger mediumflows and around which air flows. The heat pump can re-cool thegroundwater and use the heat to heat the greenhouse at night and in thewinter. This saves fuel in the case where the glasshouse is heatedduring these periods by burning fuel. The fuel savings are small andinvestment cost high whereby, without additional advantages orgovernment subsidies for saving energy, this method of operation is noteconomically feasible.

NL-A-93 01439 describes a heat exchanger with thin wires. Such heatexchangers can transfer heat in economic manner from water to air orfrom air to water, when the difference in temperature amounts to only3-5° C. What is important is that they do this while making use of anamount of electrical energy amounting to only a few percent of thetransferred heat. This means that a heat pump or cooling mechanism is nolonger necessary and energy savings are greatly improved. A considerableamount of fuel normally used for heating can be saved in this manner. Atthe time this was considered a breakthrough in climate controltechnology.

NL-C-10 12114 describes a heat exchanger with thin wires which comprisesa radial fan. This is enclosed by strips or mats of a fabric consistingof thin copper wires as warp and copper capillaries as weft, whereineach wire is soldered to each capillary in the strip or mat. Allcapillaries are connected to a water inlet manifold and a water outletmanifold, both having the form of toroidal tubes disposed around thefan. According to this known art the air is blown between the strips ormats. This therefore corresponds at least partially with the abovedescribed crossflow principle.

In order to cool greenhouses such heat exchangers can be arranged underthe layer of plants such that they do not impede the incidence ofsunlight on the plants. The cooled air from the heat exchanger must beblown upward in order to break up the inversion of hot air which tendsto float on the cold air in the greenhouse. Such heat exchangers have anumber of drawbacks however. It is difficult to control the water outlettemperature of a number of such heat exchangers when the heat exchangersare used in combination with each other. It is also difficult to controlthe water outlet temperature of different capillaries in one heatexchanger. It is however necessary to precisely control the differencein water temperature in order to store the heat from the greenhouse.According to the described prior art each heat exchanger therefore needsits own electronic unit which controls the fan speed such that it isalways possible to ensure that the temperature difference between thewater inlet and the water outlet has an optimum value. With the circulararrangement of the above described known heat exchanger the innercapillaries are subjected to a greater heat flow from the flow-by airthan the capillaries located further to the outside, such that even inone heat exchanger the problem occurs of water flows of differenttemperatures being mixed with each other.

The above described known heat exchangers require a spiral-shapedhousing which converts the radial or tangential outflow of air into anairflow in a direction such that the air displacements in the greenhousecan be controlled. The heat exchanger according to the invention needsonly a simple housing, wherein for instance on the inlet side there isdisposed a fan which generates an airflow which guides air through aheat exchanger according to the invention. In contrast to the round heatexchangers with spiral casing, these heat exchangers can be given such anarrow form that they can be placed in a long row between the columnssupporting the roof of the glasshouse. In this manner they do not takeup space which can be used for cultivation.

Claim 22 relates to a greenhouse with a heat exchanger according to theinvention.

Claim 23 provides an important further development of claim 22.

Claim 24 provides yet another development of the principle of claim 23.

A very important further aspect of claim 22 is described in claim 25.During the summer water from the aquifer can be used to cool the air inthe greenhouse, and the thereby heated water can once again be stored inthe aquifer. During the winter the stored heat is once again extractedfrom the aquifer and used to heat the air in the greenhouse.

Claim 26 relates to an air treatment plant, in particular inair-conditioning installation, with a heat exchanger according to theinvention.

Claims 27 and 28 relate to other further applications of the heatexchanger according to the invention.

The applications of the heat exchanger are not listed exhaustively inthis specification.

There now follows a description with a number of special features ofpossible applications of the heat exchanger according to the invention,requirements set in respect of the heat exchanger and the manner inwhich it can be manufactured.

It is known that closing and keeping closed a greenhouse, and therebyavoiding loss of cooling and supplied carbon dioxide, is very favourablefor the plants kept in the greenhouse. It is also possible to dispensewith the use of pesticides, irrigation water can be reused,fertilization can take place via the air, and the humidity can be heldat a desired high level. All these aspects contribute toward lowerproduction costs for the products to be yielded by the greenhouse, andan increased production.

Research in recent years has shown that a relative humidity of 90%, aCO₂ concentration of 1000 ppm, a closed roof and the installing of acooling capacity of 600 W/m² are the optimum choices for an advancedgreenhouse.

In the summer a considerably greater heat from the air in the greenhousecan be transferred to the ground water, as described in claim 25, thanis necessary to heat the greenhouse during cold nights and during thewinter season. The maximum temperature of the air in the greenhouseamounts to about 30° C., while the minimum temperature amounts to about19° C. The objective is therefore to cool, store heat and heat withoutmaking use of a heat pump. This cannot be realized using known fin-tubeheat exchangers, as has become apparent during tests at Themato ofNaaldwijk, the Netherlands, during the years 2003-2004. This objectivecan however be realized with heat exchangers of the type with thinwires, as demonstrated by extensive tests in Huissen, the Netherlands inthe period 2005-2006. The investment in a closed greenhouse isdetermined by the maximum irradiation in the summer, i.e. about 600-700Wm², which energy has to be cooled down with water that is only 10° C.colder than the air. This requires a non-trivial design on the basis ofthe heat exchanger according to the present invention.

Brief attention is now given to the heat transfer and the removal ofcondensate in glasshouses.

The Stanton number is the ratio between the coefficient of heat transferand the product of the heat capacity, the density and the velocity ofthe air. In the usual fin heat exchangers St has a value of about 0.002,considerably lower therefore than the Fanning Friction Factor f whichhas a minimum value of 0.02. It has long been thought (the so-calledChilton-Colburn relation) that St/Pr^(1/3) could never be greater thanf/2, as explained by the homology of the differential equation whichcontrols the flow resistance (based on transfer of momentum) and theheat transfer to a flat surface. If we construct a heat exchanger of thetype with thin wires with flat mats and ensure a high degree of accuracyof equidistance, it can be determined that St≧f and up to even St=2*f.It is moreover found that the St of a heat exchanger with fine wires isconstant, even with an intense condensation of water vapour on thewires, this differing essentially from a fin heat exchanger which underthe given conditions envelops itself naturally in a condensation layerwhich impedes the heat flow. For a reasonable operation of the heatexchanger this layer must be blown away at regular intervals. Acondensation film cannot form around a thin wire. A series of very smalldroplets are formed instead, such as the dew on the threads of aspider's web. When the distance between the wires has the correct value,these droplets disappear quickly in the direction of the capillaries towhich the wires are attached and are further displaced therefrom to thecondensation discharge system. This very surprising and totallyunexpected result, which has in the meantime been ascertained inpractice in a greenhouse and confirmed by measurements, implies that thecoefficient of heat transfer reaches a value of 500 W/m²K, which must becompared with the corresponding value of only 25 W/m²K of a tube-finheat exchanger.

Attention is now briefly paid to the heat transfer of water to copper.For practical and economic reasons the capillaries to which the thinwires are attached have an outer diameter in the order of 2 mm and aninner diameter of 1 mm. See claim 12 in this respect. In a warm andhumid greenhouse with an economic air velocity of several metres persecond in the heat exchanger, the necessary heat transfer between thecooling water and the inner wall of these capillaries, as well as theheat conduction along the thin wires, require a centre-to-centredistance between the capillaries in the order of only 4 to 6 mm. Thismakes weaving of the wires unattractive, since a weave intersection willoccur between each set of nearby capillaries. At this position the wireslie very closely to each other, this resulting in a low heat transfer tothe flow-by air. It is therefore considerably more effective for thewires to extend in two groups parallel to each other on either side ofthe capillaries, whereby the intersections of a fabric are avoided.

A considerable part of the cost of a cooler for a greenhouse is for themedium-tight insertion of the thousands of capillaries in a sub-manifoldfor the purpose of connecting them to the medium flow, normally a waterflow. For economic reasons each manifold can be embodied as aninexpensive polyethylene tube. An effective construction is specified inclaim 11. PE is a very cheap and highly usable material. Some smallleakage from a greenhouse to the atmosphere is not a problem; water isafter all available in abundance.

It is a further advantage to choose the diameter of each sub-manifold,i.e. a manifold of one heat exchanger, so that it is the same as thedesired centre-to-centre distance of the mats. The sub-manifolds lyingtightly against each other can hereby together form the wall of the airduct. Reference is made in this respect to claims 17 and 18.

It has been found very advantageous to make use of the difference intemperature between the ingoing and outgoing water necessary to storethe heat underground, and also to realize a great difference intemperature of the inflowing and the outflowing air. This reduces theairflow and thereby the necessary fan capacity, improves thecondensation by decreasing the air temperature below the dew point, andequalizes the difference in temperature between water and air over thewhole heat exchanger.

This effect can be realized in accordance with claim 5 by blocking thewater flow (in fact generally the medium flow) in the pipes of thesub-manifolds a total of three to five times on both sides of the mat inorder to force the water flow in effective counter-flow relative to theairflow. The optimum number of theoretical units or N_(TU) of the heatexchanger is about 1, and if the flow is blocked more than once theblocks can leak a little without reducing too much the. effectiveN_(TU). It is essential to block an odd number of times in order torealize two open ends on one sub-manifold and two closed ends on theother.

The centre-to-centre distance between the sub-manifolds equals thediameter of the sub-manifolds, and this has the result that it is notpossible to connect all sub-manifolds to the same two main inlet andoutlet manifolds. It is necessary to make use of four manifolds, i.e.two inlet manifolds and two outlet manifolds, such that there is spacebetween the holes which mutually connect the ends of the sub-manifolds.The main manifolds can likewise be manufactured from a plastic, such asPE, with perforations having a smaller diameter than the outer diameterof the sub-manifolds, whereby these sub-manifolds can be pressed intothese perforations. This is a very simple connection that has provenitself in drip irrigation technology.

Brief attention is now paid to the inhibition of corrosion. In countrieswith scarcity of water a greenhouse is often irrigated by means of theeffluent from a water treatment plant for the waste water of a city.This effluent comprises volatile ammonia which corrodes the tin-coveredwires. This corrosion is prevented when the airflow moves upward. Thecondensation flow always moves downward and in this case thecondensation always keeps the foremost end of the heat exchanger incleaned state, thereby preventing ammonia-catalyzed corrosion.

Several aspects of the application of the heat exchanger according tothe invention in heat pump systems is now briefly discussed.

The “Coefficient of Performance” (COP) of a heat pump such as is usedfor air-conditioners and sometimes for space heating systems, is greatlydependent on the temperature drop over the heat exchangers of theevaporator and the condenser.

Heat exchangers known heretofore cannot be used directly for the mediaof condensing or evaporating heat pumps. Flat copper manifolds cannotwithstand the occurring high pressures and for safety reasons theconnections between the capillaries and the manifolds must therefore berealized by hard-soldering. See claim 9 in this respect.

For pressures of more than 4 bar a metal manifold is required in theform of a round tube to which the capillaries are connected byhard-soldering at a temperature of for instance 500° C. This cannot berealized with capillaries of only 15 cm long, since there are simply toomany ends requiring a hard-soldering operation. Also underlying theinvention therefore is the objective of solving this problem. Thissolution has been found in the measures according to claim 6. The flowof medium is considerably smaller than in the case of water with adifference in temperature between the inlet and outlet of severaldegrees Celsius, since the volume of latent heat or cold is so muchgreater. Even if the capillary is many metres long, the pressure drop inthe two-phase medium still does not impede good operation of the heatexchanger.

On the basis of these long tubes curved in a zigzag it is not possibleto use a weaving process to arrange the wires. The width of the weavingmachine is not large enough and weaving of a long capillary back andforth to a weft of more than 1000 thin wires is technically impossibleat this moment. It is therefore necessary to model the long capillarytube into a zigzag construction of mutually parallel, equidistantlyplaced capillaries in order to cover a space of for instance 15×15 cmwith a centre-to-centre distance between the capillaries of for instance12 mm, whereby a mat with only two end zones is realized instead of amat with thirty end zones to which should be connected manifolds eachhaving thirty perforations. These end zones are stripped of tin inanodic manner in an acid or base environment and then connected byhard-soldering to the relevant manifold.

The mat can then be connected by hard-soldering to the thin round coppertubes which carry the working medium to and from the compressor.

All air-conditioners operate to date with tube-fin heat exchangers.These have, hard copper tubes of a large diameter. They would otherwisebuckle under the compression forces necessary to press the aluminiumfins onto the tubes. The evaporator and the condenser thus have a veryconsiderable volume of working medium. For safety reasons this largequantity of working medium may not be flammable. Use is made for thisreason of fluorinated and even chlorinated compounds which are howeverproblematic due to environmental considerations. In a thin wire heatexchanger according to the invention there are no thick tubes and, dueto the low volume, use can be made of propane or butane, and the totalactive volume of working medium can be reduced to minimal proportions,for instance the amount of a holder for filling lighters, which arecommercially available everywhere and are so small they are deemedcompletely fireproof. A very small volume of the heat exchanger isobtained particularly with the construction according to claim 6.

A mat of for instance 15×15 cm² which is only connected at its two thinends is mechanically not sufficiently stable. All 180° bends between theadjacent capillaries must be fixed. For this purpose a rigid structureis used which holds the mat in its place. Reference is made in thisrespect to claims 7 and 19.

Finally, brief reference is made to several aspects relating to districtheating.

In cold, densely populated countries district heating is a veryefficient method of heating space. The waste heat in electricitygeneration is herein used at the lowest possible temperature, whereinthe houses or user stations act as condensers for the steam turbines.The return temperature of district heating networks nowadays is about 40to 50° C. It would be very advantageous if it were possible to lowerthis temperature to for instance 25° C. It would then be possible toheat twice as many houses with the same water, and the steam pressure inthe condenser would be lowers which increases the efficiency ofelectricity generation. These wishes can also be realized with a heatexchanger according to the present invention.

The feed temperature of the water of a district heating system is often100° C. The return temperature can be designed at 25 to 27° C. Thetemperature difference therebetween is great enough to use very longcapillaries and to give the heat exchanger the same form as those whichcan be used for direct connection to the evaporator or condenser of anair-conditioner.

Long tubes such as are applied in district heating are subject topressure shocks. The heat exchanger according to the invention in theembodiment according to for instance claims 6 and 9 can withstand veryhigh pressures.

Using the described construction the air can be heated to for instance50° C. and the N_(TU) can be designed for this requirement, whereby theairflow necessary to extract the necessary heat from the heat exchangeris very small and the fan can be very low-noise. With a view tocompatibility with the available indoor space, the heat exchanger can bedesigned in a slender form, for instance 15 cm wide, 1 meter long and 15cm high, and a slow-rotating, silent crossflow fan can be applied.

The invention will now be elucidated with reference to the accompanyingdrawings. In the drawings:

FIG. 1 shows a partly cut-away perspective view of a heat exchangeraccording to the invention;

FIG. 2 shows a schematic cross-section through the heat exchanger ofFIG. 1;

FIG. 3 is a perspective view of a detail of a heat exchanger mat in afirst embodiment, wherein a number of wires are omitted for the sake ofclarity;

FIG. 4 shows the cross-section IV-IV of FIG. 3;

FIG. 5 is a perspective view corresponding with FIG. 3 of a variant;

FIG. 6 shows the cross-section VI-VI of FIG. 5;

FIG. 7 is a perspective view of a heat exchanger mat in which groups ofcapillaries are ordered in zigzag manner;

FIG. 7A shows in longitudinal section the detail of FIG. 7 indicatedwith an arrow;

FIG. 8 shows a view corresponding with FIG. 7 of a variant;

FIG. 8A shows in longitudinal section the detail of FIG. 8 indicatedwith an arrow;

FIG. 9 shows a view corresponding with FIGS. 7 and 8 of a furtherembodiment;

FIG. 10 is a schematic cross-section through a part of a greenhouseaccording to the invention; and

FIG. 11 is a schematic representation of application of a cooling systemwith a heat exchanger according to the invention.

FIG. 1 shows a heat exchanger 1 according to the invention. This heatexchanger 1 has a housing 2 with an air inlet 3 and an air outlet 4. Anaxial fan 5 is disposed in air inlet 3.

Two water inlet manifolds 6 and two water outlet manifolds 7 are presentin housing 2. Manifolds 6 and 7 are connected via respectivesub-manifolds 91, 92 to capillaries 8 disposed in groups in the mannerof mats. Capillaries 8 which extend from inlet manifold 91 and to outletmanifold 92 are connected to an intermediate manifold 9 servingrespectively as outlet manifold and inlet manifold. Reference is alsomade in this respect to FIG. 2. This figure also makes clear the mannerin which the air 63 is blown by the axial fan 5 into housing 2 via gasinlet 3. The air flows along capillaries 8 and leaves housing 2 via gasoutlet 3, see arrow 64. The water flowing through the capillaries isheated by the air 63, 64, and this air is in turn cooled by the water.It is noted that for the sake of clarity in FIGS. 1 and 2 the thinwires, which form an essential component of the heat exchanger accordingto the invention, are not drawn. Reference is made in this respect tothe figures to be described below.

FIG. 3 shows a part of a heat exchanger mat according to the invention.Capillaries 8 are ordered mutually parallel and equidistant with acentre-to-centre distance of about 12 mm. Thin wires 10 are placedinterwoven with capillaries 8.

FIG. 4 clarifies the configuration. The centre-to-centre distancebetween adjacent, correspondingly placed wires 10 can be equal to orgreater than the diameter of wires 10.

FIGS. 5 and 6 show an alternative in which wires 10 are not placedinterwoven but are arranged in two groups and in mutually parallelrelation on both sides of capillaries 8.

It will be apparent that a weaving operation is necessary in theconfiguration according to FIGS. 3 and 4. This is relatively slow andmakes mass production of the heat exchanger problematic. Simpler tomanufacture is the heat exchanger in the configuration according toFIGS. 5 and 6. It would appear at this moment that this is more suitablefor mass production.

Capillaries 8 consist of copper and are provided on their outside with atin layer. The wires are also of copper and provided with a tin layer. Asoldering operation with local heating is therefore sufficient torealize in a short time an intensively metallic, heat-transferringcontact between the capillaries and the wires.

It is important to note that the centre-to-centre distance betweencapillaries 8 in FIGS. 3, 4 must be greater than the centre-to-centredistance between capillaries 8 in FIGS. 5, 6. This is because theweaving operation for a construction as according to FIGS. 3 and 4imposes a technically determined lower limit. This lower limit does notexist in the configuration of FIGS. 5 and 6. The heat exchanger based onFIGS. 5 and 6 can hereby be dimensioned more easily in accordance withselected design standards.

FIG. 7 shows that capillaries 8 are inserted into tin-plated coppertubes serving as manifolds. They are connected thereto bysoft-soldering. Heat exchanger mat 21 as according to FIG. 7 comprisesfour sections 22, 23, 24, 25. An inlet manifold 26 is connected to fivecapillaries 8 in which medium flows in the direction of an arrow 127 toa manifold 27, which is also connected to a group of five capillaries 8of section 23 in which the medium flow takes place as according to anarrow 128, so in opposed direction, to a manifold 29, then via fivecapillaries to a manifold 30 of section 24, from here to section 25 andfive capillaries to an outlet manifold 31. The medium inlet is indicatedwith an arrow 32; the medium outlet is indicated with an arrow 33. Themedium flows in the manifold tubes are also indicated with arrows. Theairflow is designated with the reference numeral 64. The air flows oneither side of mat 21 in longitudinal direction of wires 10.

FIG. 7A is an enlarged detail in cross-section which shows that thereare interruptions between manifold tubes lying in one line. At theposition of these interruptions the tubes in question are closed byplugs, generally designated with 34. Tubes 27 and 30 are also closed atthe ends with such plugs.

FIG. 8 shows a functionally corresponding variant. The drawn heatexchanger mat 35 functions in the same manner as mat 21, but themanifold tubes 41 and 42 consist of polyethylene or other thermoplasticmaterial with a low heat conduction. During the production process eachof the tubes is cut open on one side in longitudinal direction,whereafter the ends of capillaries 8 are placed in the cuts and thematerial of the tube is then melted at that position by local heatingsuch that in the manner shown in FIG. 8 capillaries 8 are connectedsubstantially sealingly to both manifold tubes 41, 42. Instead of theinterruptions and the plugs 34 in the embodiment according to FIG. 7A, aplug 43 is inserted locally as according to FIG. 8A. The ends of tube 41are also closed by respective plugs.

FIG. 9 shows a heat exchanger mat 51 in an important alternativeembodiment. In this embodiment capillaries 8 are formed from onecapillary tube modelled into a zigzag shape, wherein each end of eachcapillary is connected via a U-shaped curved part 52 to the end of anadjacent capillary. These U-shaped curved parts of both sides of mat 51are in register and connected mechanically to each other by means ofrespective strengthening profiles 53, 54 with a low heat conduction, forinstance of plastic.

The inlet zone 101 and outlet zone 102 of the capillary tube formingcapillaries 8 and the U-shaped parts 52 are connected inpressure-resistant manner by hard-soldering to respective manifolds (notdrawn), to which further heat exchanger mats are also connected in thesame manner.

FIG. 10 shows a greenhouse 11 with heat exchangers according to theinvention. Greenhouse 11 has a floor 12 on which plants 95 stand in potsor are supported at a distance from floor 12 by for instance rollertables 61. Plants 95 define a leaf canopy which depends on the nature ofthe plant and the stage of its growth. The diverse leaf canopies areshown generally with broken lines, all marked 62 for the sake ofconvenience. It will be apparent that a leaf canopy cannot be definedwithin close limits and can display considerable height differencesbetween plants, and even within one leaf canopy.

Greenhouse 11 has a translucent, preferably transparent roof 13 throughwhich sunlight 96 can radiate onto leaf canopies 16. Heat exchangers 1as according to FIG. 1 are disposed between plants 95. In thisembodiment air 63 is drawn in from close to floor 12 with these heatexchangers 1, guided along the heat-exchanging mats (see FIGS. 1 and 2)and cooled or heated by the water flowing therethrough via the thin,vertically extending wires 10 along which the air flows in longitudinaldirection. The air is then blown upward as according to arrows 64 to theupper part of glasshouse 11.

It is however also possible to use the heat exchanger without fan 5,i.e. by applying a chimney-like housing, one end of which extends intothe upper part of glasshouse 11 and the other end of which is situatedclose to floor 12. With such a housing a natural draught can occur,thereby saving the energy for driving a fan 5.

FIG. 11 shows a detail of a greenhouse, wherein a gutter 71 is presentat the position of a transition between the transparent roofs 13. A tube72 consisting of foil and having a row of perforations 73 is positionedunder this gutter. The tube is inflated by the exhaust gases from a gasturbine used for heat-power coupling. In a gas turbine these gases haveonly 4% CO₂, so there is much gas available which can have a pressure of3600 Pa at the outlet of the turbine. This corresponds to an outflowspeed of about 50 m/s. The air in question flows out of perforations 73as according to arrows 74 and into a “reverse chimney” 75, in the topside of which is situated a heat exchanger 76 according to theinvention. The construction thereof corresponds largely to that of theheat exchanger according to FIG. 7. Via a cooling water feed conduit 77cooling water is admitted on the underside, heated and discharged aslukewarm water via a water outlet 78. The reverse chimney 75 consistsfor instance of a polyethylene foil.

Due to the natural downward draught and the support thereof by theoutflowing gases 74 there occurs an effective cooling of the hot airdrawn in from the top side of the greenhouse, see arrows 79, and cooledair is blown out at the bottom as according to arrows 80.

1-28. (canceled)
 29. A heat exchanger, comprising: a housing with a gasinlet and a gas outlet, for exchanging heat between at least one of aliquid-containing medium and a liquid-vapor mixture, and a gas; a mediuminlet; a medium outlet; and at least one substantially flat heatexchanger mat, wherein the mat comprises: a plurality of capillaries ofheat-conducting material disposed in mutually parallel and mutuallyequidistant relation; and a plurality of wires of heat-conductingmaterial, wherein the wires are attached in heat-conducting contact tothe capillaries, extend in mutually equidistant relation in a transversedirection relative to the capillaries and have a mutual distance betweeneach wire in the order of magnitude of the diameter of the wires;wherein under the influence of a drive means, the gas can flow along thewires for heat exchange between the gas and the medium flowing throughthe capillaries via the walls of the capillaries and the wires, whereinthe heat exchanger is embodied such that the gas flows in a longitudinaldirection of the wires along each mat and that at least a substantialpart of the gas is prevented from flowing through the mat.
 30. The heatexchanger as claimed in claim 29, further comprising an inlet manifoldand an outlet manifold, wherein the capillaries extend between the inletmanifold and the outlet manifold so that medium can flow therethrough.31. The heat exchanger as claimed in claim 29, wherein the wires contactadjacent capillaries alternately on a first side and on a second side ofthe capillaries, wherein adjacent wires or groups of wires contact theopposite sides of the capillaries relative to nearby wires or groups ofwires, such that the wires or groups of wires are mutually interwoven.32. The heat exchanger as claimed in claim 29, wherein two groups ofwires extend in two main planes in mutually parallel relation to eachother, wherein the wires of each group contact the same side of thecapillaries.
 33. The heat exchanger as claimed in claim 30, wherein theinlet manifold has at least one of an interruption and plug, the outletmanifold has at least one of an interruption and plug placed offsetrelative to the inlet manifold such that the medium admitted through aninlet of the inlet manifold is guided successively through a first inletmanifold, a first group of capillaries connecting to the first inletmanifold, a first intermediate manifold, a second group of capillariesand so forth, and finally through the outlet manifold such that themedium moves in one direction in a zigzag manner by moving through eachgroup of capillaries in the opposite direction of the previous group ofcapillaries.
 34. The heat exchanger as claimed in claim 29, wherein thecapillaries are formed from one capillary tube modeled into a zigzagshape, wherein each end of each capillary is connected via a U-shapedcurved part to the end of a nearby capillary, wherein end zones of thecapillary tube are connected to respective tubes acting as manifolds.35. The heat exchanger as claimed in claim 34, wherein the U-shapedcurved parts of both sides of the mat are in register and coupledmechanically to each other by means of a strengthening profile with alow heat conduction.
 36. The heat exchanger as claimed in claim 30,wherein each manifold is a tube having a row of perforations and whereinthe ends of the capillaries are sealingly inserted into theperforations.
 37. The heat exchanger as claimed in claim 29, whereineach manifold is a tube of thermoplastic material, the tube having a cutin a longitudinal direction on one side, whereafter the ends of thecapillaries are placed in the cut and the material of the tube is thenmelted at that position by local heating such that the capillaries areconnected substantially sealingly to the tube.
 38. The heat exchanger asclaimed in claim 37, wherein the main flow direction of the medium isopposed to the flow direction of the gas.
 39. The heat exchanger asclaimed in claim 29, wherein the heat exchanger comprises a plurality ofheat exchanger mats held by spacers in mutually parallel and equidistantrelation.
 40. The heat exchanger as claimed in claim 39, wherein thespacers are inlet manifolds and outlet manifolds, wherein thecapillaries extend between each inlet manifold and each outlet manifoldso that medium can flow therethrough.
 41. The heat exchanger as claimedin claim 35, wherein the heat exchanger comprises a plurality of heatexchanger mats held by spacers in mutually parallel and equidistantrelation, wherein the spacers are the strengthening profiles.
 42. Theheat exchanger as claimed in claim 29, wherein the gas is driven by fanmeans.
 43. The heat exchanger as claimed in claim 29, wherein thehousing is adapted to serve as a chimney such that the gas is driven bynatural convection.
 44. A greenhouse, comprising: a ground surface;plants supported by the ground surface by support means and forming aleaf canopy; heating and cooling means with at least one heat exchangercomprising: a housing with a gas inlet and a gas outlet, for exchangingheat between at least one of a liquid-containing medium and aliquid-vapor mixture, and a gas; a medium inlet; a medium outlet; and atleast one substantially flat heat exchanger mat, wherein the matcomprises: a plurality of capillaries of heat-conducting materialdisposed in mutually parallel and mutually equidistant relation; and aplurality of wires of heat-conducting material, wherein the wires areattached in heat-conducting contact to the capillaries, extend inmutually equidistant relation in a transverse direction relative to thecapillaries and have a mutual distance between each wire in the order ofmagnitude of the diameter of the wires; wherein under the influence of adrive means, the gas can flow along the wires for heat exchange betweenthe gas and the medium flowing through the capillaries via the walls ofthe capillaries and the wires, wherein the heat exchanger is embodiedsuch that the gas flows in a longitudinal direction of the wires alongeach mat and that at least a substantial part of the gas is preventedfrom flowing through the mat, wherein one of the gas inlet and the gasoutlet is situated above the level of the leaf canopy and the other issituated below the level of the leaf canopy, or both are situated in theleaf canopy.
 45. The greenhouse as claimed in claim 44, furthercomprising a heat storage for temporarily storing surplus heat.
 46. Thegreenhouse as claimed in claim 45, wherein the heat storage is of thestratified type.
 47. The greenhouse as claimed in claim 44, wherein theheating and cooling means are adapted for connection to an aquifer. 48.A city heating system, comprising: a plurality of heat exchangersinstalled with a plurality of users, the heat exchanger comprising: ahousing with a gas inlet and a gas outlet, for exchanging heat betweenat least one of a liquid-containing medium and a liquid-vapor mixture,and a gas; a medium inlet; a medium outlet; and at least onesubstantially flat heat exchanger mat, wherein the mat comprises: aplurality of capillaries of heat-conducting material disposed inmutually parallel and mutually equidistant relation; and a plurality ofwires of heat-conducting material, wherein the wires are attached inheat-conducting contact to the capillaries, extend in mutuallyequidistant relation in a transverse direction relative to thecapillaries and have a mutual distance between each wire in the order ofmagnitude of the diameter of the wires; wherein under the influence of adrive means, the gas can flow along the wires for heat exchange betweenthe gas and the medium flowing through the capillaries via the walls ofthe capillaries and the wires, wherein the heat exchanger is embodiedsuch that the gas flows in a longitudinal direction of the wires alongeach mat and that at least a substantial part of the gas is preventedfrom flowing through the mat.